The One Nation senator says said he wrote to British authorities in June 2016, just days before nominations closed saying he did not believe he was a British citizen, but “just in case I am, I renounce it, effective immediately”.

Section 44 of the Constitution bars people with citizenship in a country other than Australia from standing for election.

Roberts is one of seven politicians – six senators and an MP: deputy prime minister Barnaby Joyce, deputy Nationals leader Fiona Nash, former minister senator Matt Canavan, former Greens senators Scott Ludlam and Larissa Waters, and NXT senator Nick Xenophon, – before the High Court on the issue

Today, Roberts, who has been emphatic about his sole Australian citizenship, despite mounting evidence to the contrary, was quizzed in the High Court in Brisbane today, and his responses contained several surprising revelations.

Roberts signed his citizenship form, which said he was a British citizen, without reading it.

He thinks, based on the handwriting, that his teenage sister filled in his form.

He’d sign “whatever my father gave to me”.

He believed he was Australian because is father “would have ribbed me for sure if he knew I was British”.

Emails he sent last year to UK officials about his British citizenship went to two invalid addresses.

The first email was sent to a “.uksydney” address in May. It was a nonexistent domain.

He sent a second email to a different address in June complaining about a lack of response.

That account closed in 2010.

His counsel, Robert Newlinds, said Roberts “didn’t believe he was [a British citizen] but suspected he might be when he nominated to be a senator”.

Newlinds argued the emails issue is irrelevant and “inadmissible”.

Roberts claimed he was raised from birth to believe he was Australian.

Contrary to his earlier claims that he’d never been the citizen of another country, he was automatically Indian by birth, but that was renounced in 1974 when he became an Australian citizen as a teenager.

The future of the One Nation senator’s political career now hangs on the details of what happened when, with with the Commonwealth solicitor-general saying the Crown would press for his disqualification if they were dated after his nomination.